Chemotaxis, the movement of an organism toward or away from various chemicals, is a simple behavior found in nearly all forms of life. The chemotactic behavior of the simple bacterium Escherichia coli is a useful model with which to investigate the molecular details of chemoreception and sensory transduction. The objective of the proposed research is to determine the complexity of the chemotasix machinery in E. coli and to elucidate the ways in which stimulus information is processed and transmitted to the flagella, the motor organelles. The major experimental approach to this problem will combine genetic analysis with physiological studies of various chemotaxis-defective mutants. Chemotaxis components will be identified through isolation of nonchemotactic mutants. The interactions among gene products will be studied by reversion analysis. The nature of the communication link between chemoreceptors and flagella will be examined through physiological studies of conditionally-defective mutants.